This invention relates to a method for reinforcing existing concrete structures.
In many cases, various existing concrete structures require reinforcement against earthquake, because they were constructed under old design standards and guidelines, and thus are inferior in their aseismatic performance in comparison with those concrete structures constructed by the current standards. Also, in many cases, such reinforcement of the existing concrete structures is necessary for the sake of increasing the number of storeys of the buildings at the time of extending and/or remodelling them so as to be more durable against the designed load.
As the typical method for reinforcement against the earthquake according to the conventional technique, there have been proposed various ones, according to which the existing column members are enclosed with steel plates, or such existing column members are enveloped with welded metal nets or reinforcing steel cages, in an attempt to improve, in the main, toughness of the column members, i.e., in an effort not to reduce the loading capability and the energy absorbing capability, even if such structural elements are subjected to a certain degree of damages such as cracks, etc.
These reinforcing methods, however, are not free from various points of problem such that they inevitably necessitate the welding work of the steel plate at the construction site, and, in order to obtain the desired reinforcement, the welding work must be done by skilled welders; that transportation of steel plates into the existing building is difficult to be attained by the use of heavy machinery, and cutting these steel plates into a size which can be carried by man power would inevitably increase the amount of welding work at the construction site; and that it is also necessary to pour mortar between the existing column members and the steel plates, the welded metal nets, or the reinforcing steel cages to attain transmission of stress between them, but it has been difficult to charge such mortar to a sufficiently dense and compact degree.
Furthermore, the above-mentioned reinforcing methods contributes generally to increase only the shear strength of the existing column members, and, in order to bring their bending strength to a degree which is as equal as before the reinforcement, it is necessary to provide slits in the reinforcing members such as steel plates, etc. However, with such slits being formed in the reinforcing members which are to be exposed to the outer surface of the building construction, water-tightness at these slitted portion would become inferior with the consequence that troubles to derive from water leakage tend to arise not infrequently. In addition, necessity arises for treatment of the steel plates against rust, which, in turn, would inevitably increase maintenance cost.
There has also been proposed a method, in which the bending strength of the concrete structure is reinforced by attaching steel plates onto it by use of both anchor bolts and adhesive agent or grout. This method, however, is not always satisfactory in respect of both cost and working period for the reinforcement.
There has also been proposed another reinforcing method, in which high mechanical strength fiber in the form of a fiber-reinforced plastic (FRP) is attached to the concrete structure with use of adhesive agent. This method of working, however, has its own point of problem such that the pre-fabricated fiber-reinforced plastic components are required to be adhered at the construction site, on account of which, when the object to be reinforced is large in size, the FRP component must be divided into small sub-components for the construction. Moreover, depending on the configuration of the object to be reinforced, the work inevitably becomes complicated.